Endodontic instrument

ABSTRACT

The present invention disclosed herein is directed to improved endodontic dental instruments for extirpating and/or obturating a root canal. The dental instruments of the invention have at least one friction reducing element which assists in the removal of material from a tooth canal and which reduces frictional loads on the instrument during extirpating and obturating procedures.

This application is a Divisional of Ser. No. 08/570,283, filed Dec. 11,1995.

FIELD OF INVENTION

The invention relates generally to the field of endodontics and moreparticularly to reamers and condensers used in performing root canalprocedures. The reamers are used to remove diseased tissue from thecanal and the condenser is used to place sealing and filling material inthe prepared canal cavity after removal of the diseased material.

BACKGROUND OF THE INVENTION

The circulatory and neural systems of the tooth enter the tooth at theterminus of each of its roots and extend through a narrow, tapered canalsystem to a pulp chamber adjacent the crown portion of the tooth. If thepulp tissue becomes diseased, extraction of the tooth can often beavoided by removing the diseased tissue and sealing the canal system inits entirety. Endodontic files and reamers are tapered instruments usedto remove the diseased tissue in the root canal by reciprocating and/orrotating the instruments in the canal. Since many root canals are small,curved and calcified, the instruments must be able to withstand thetorsional load necessary to enlarge the canal without breaking theinstrument thus further complicating the treatment.

Once as much of the diseased material as practicable is removed from theroot canal, the canal is sealed closed, typically by reciprocatingand/or rotating a condenser instrument in the canal to urge a sealingmaterial such as gutta-percha into the canal. Gutta percha used as asealing material has a high viscosity and thermoplastic character andsince the canals are usually small and curved, it is also desirable touse a condenser instrument which is able to withstand the torsional loadnecessary to urge the material into the canal without breaking theinstrument while at the same time condensing the sealing materialwithout leaving any voids in the canal which may lead to treatmentfailure.

One of the problems with traditional endodontic instruments used forextirpating and filling a root canal is that the torsional limitationsof the instrument are often exceeded resulting in breakage of theinstrument. Breakage of the instrument may occur as a result of theinadequate removal of dental chips which are cut from the wall of theroot canal. The dental chips may be engaged between the instrument andthe root canal wall resulting in friction which may cause excessivetorque and thus breakage of the instrument.

Traditional reamers or files contain helical flutes along the workingportion which are substantially semi-circular in cross-section, that is,an arc tracing a line transverse to the flute length along the bottom ofthe flute wall is of substantially uniform radii at all points along theline. This structure is intended to promote advancement of tooth chipsand debris up the expanding diameter of the instrument along thespiraling flute away from the tip. However, during the extirpatingprocedure, the dental chips which are formed may be inadequately removedfrom the root canal and may be forced into flutes along the instrumentbetween the instrument and the root canal causing damage to the canalwalls and/or inadequate or uneven tissue removal. This build up ofdebris may also lead to increased friction resistance already imposed bycontact between the instrument and the canal, which in turn increasesthe torsional load on the instrument. In many cases, the torsional loadson the instrument exceed the tensile strength of the working portion ofthe instrument resulting in fracture.

It is therefore an object of the invention to provide an endodonticdental instrument which reduces the friction load on the instrument inthe root canal.

It is another object of the invention to provide an endodontic dentalinstrument having a reduced tendency to break during use.

Still another object of the invention is to provide a condenserinstrument which more effectively, introduces and condenses a sealingmaterial into an extirpated root canal.

Yet another feature of the invention is to provide a reamer which moreeffectively removes damaged or diseased tissue from a root canal, thusdecreasing friction during root canal cleaning and extirpation andimproving the uniformity of the tissue removal from all affectedportions of the canal and its defining wall.

SUMMARY OF THE INVENTION

With regard to the foregoing and other objects, the present invention isdirected to an improved endodontic instrument which comprises anelongate working portion, which may be tapered or of substantiallyuniform cross-sectional diameter, extending between adjacent a base orproximate end and adjacent a tip or distal end. The working portion hasa length of from about 3 to about 18 millimeters and a peripheraldiameter ranging from about 0.08 millimeters to about 1.9 millimeters,and includes at least one helical flute, at least one helical landadjacent the flute in working cooperation therewith with a tissueremoving edge therebetween and a point distal from the tissue removingedge, each flute and land having a pitch ranging from about 1 spiral per16 millimeters to about 1 spiral per millimeter for use in an endodonticprocedure. The working portion is adapted through provision of one ormore friction reducing elements to reduce friction between theinstrument and the canal to improve the performance of the instrumentwhile reducing the tendency of the instrument to fail under torsionalstresses.

In one friction reducing embodiment, the point distal from the tissueremoving edge adjacent the periphery, in cross-section, recedes from theperiphery at from about an acute angle with respect to a line tangent tothe periphery at the point of intersection. The angle is measured fromthe side of the tangent line distal from the tissue removing edge.

In another embodiment, the endodontic instrument has at least one outerland, when viewed in cross-section, adjacent the periphery defined bythe tissue removing edge and at least one recessed land. The outer landand the recessed land may be adjacent one another or separated by atleast two flutes.

In yet another embodiment, the endodontic instrument comprises at leasttwo flutes spaced apart by a tissue removing edge or a land which fluteshave substantially unequal dimensions when viewed in cross-section. Theflutes are parallel along the working length meaning that they extendalong helical paths that do not intersect each other. An endodonticinstrument of the invention may also comprises a combination of two ormore of the foregoing friction reducing elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill now be further described in the following detailed description inconjunction with the accompanying drawings in which:

FIG. 1 is an elevational view of a reamer instrument according to oneembodiment of the invention;

FIG. 2 is a cross-section view of the reamer instrument of FIG. 1 takenalong line B--B thereof;

FIG. 3 is a longitudinal view in section of the reamer instrument ofFIG. 1 taken along line A--A thereof;

FIGS. 4A-C through 16A-C are elevational, longitudinal andcross-sectional views of various designs of endodontic instrumentsaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-16 illustrate endodontic instruments having various workingportion configurations within the scope of the invention. Theinstruments may be used as reamers or condensers depending on thedirection of twist of the helical flutes and lands with respect to thedirection of rotation of the instrument.

In all of the embodiments of the invention illustrated herein, theinstruments are represented as reamers. However, it will be appreciatedthat a mirror image of the instrument design may be used as a condenserfor the same direction of rotation of the instrument. Condenserinstruments made in accordance with the invention are used to fill voidspaces in the root canal cavity. In all of the embodiments havingmultiple flutes, and as shown in the drawings, the flutes are parallel,i.e., they extend along helical paths that do not intersect each otheralong the working length.

With reference now to FIG. 1, there is illustrated an endodonticinstrument according to one embodiment of the invention which may beused as a reamer and which has a shaft 10 having a base or proximate end12 and an elongate working portion 14 extending between the base orproximate end 12 terminating in a tip or distal end 16. The proximateend 12 also contains a fitting portion 18 for mating with a chuck of adental handpiece (not shown). Alternatively, or in addition to thefitting 18, the proximate end 12 may include a knurled or otherwisetreated surface to facilitate hand manipulation of the reamer 10. Theworking portion 14 of the instrument has a length which may range fromabout 3 millimeters to about 18 millimeters. A preferred length is about16 millimeters.

The working portion may have the same cross-sectional diameter betweenthe proximate end 12 and the distal end 16 or the working portion may betapered in either direction from the proximate end 12 to the distal end16. When tapered, the taper of the cross-sectional diameter of theworking portion 14 may range from about -0.01 to about 0.8 millimetersper millimeter, preferably from about 0.02 to about 0.06 millimeters permillimeter.

The working portion 14 is comprised of one or more helical flutes 20 andone or more helical lands 22 (one each in the embodiment of FIG. 1). Inthe illustrated embodiment, helical flute 20 and helical land 22 areadjacent tissue removing edge 24. Helical land 22 and tissue removingedge 24 are at the periphery of the working portion 14 while flute 20has a surface 26 (FIGS. 2 and 3) which is recessed from the periphery ofthe working portion 14 which surface, in cross-section, recedes from theperiphery 28 at from about an acute angle 27 with respect to a line 29tangent to the periphery at the point of intersection B which angle ismeasured from the side of the tangent line 29 distal from the removingedge 24.

As shown in FIGS. 2 and 3, tissue removing edge 24 is generally oppositea portion of the helical land 22. The wall of flute 20 intersects theperiphery of the working portion in the region denoted by the letter Aimmediately adjacent the periphery 28 of the working portion at an angleof about 90 degrees to tangent to form what is commonly referred to as azero or neutral rake angle from the perspective of the surface 26 of theflute 20. For purposes of this invention, the rake angle of the tissueremoving edge 24 may be neutral, positive or negative but is preferablyabout neutral.

It will be appreciated that helical land 22 presents a bearing surfacebetween tissue removing edge 24 at point A and point B distal from thetissue removing edge (FIG. 2) so that when rotated in a canal, only edge24 removes tissue while the bearing surface of the helical land 22 bearsagainst the canal wall. In FIG. 2, both point A and point B are locatedat the periphery 28 of the working portion 14 on generally opposingsides of the land 22.

As illustrated by FIGS. 2 and 3, flute 20 has a concave surface 26 whichis recessed from the periphery of the working portion, so that at pointB, the surface 26 forms about an acute angle 27 with the line 29 tangentto the periphery. By providing a flute having about an acute angle at B,tissue and debris from the root canal may be more effectivelytransported and removed from the canal in a direction opposite to thedirection of travel of the instrument as the instrument is rotated inthe root canal. By removing the debris more effectively from the rootcanal, there is less friction on the working portion and thus lesstendency to shear the instrument by the torque applied to theinstrument.

For the most effective cutting and tissue removal it is preferred thatthe pitch of the helical flutes 20 and helical lands 22 range betweenabout 1 spiral per 16 millimeters to about 1 spiral per millimeter alongthe working portion 14 of the instrument.

Another endodontic instrument 10 according to the first embodiment ofthe invention is illustrated in FIGS. 4A-C wherein FIG. 4A is anelevational view, FIG. 4B is a cross-sectional view along line B--B ofFIG. 4A and FIG. 4C is a partial longitudinal view of FIG. 4A takenalong line A--A thereof. The working portion 14 of the instrumentillustrated by FIGS. 4A-C contains two helical flutes 32 and 34 and hastissue removing edges 36 and 38 adjacent two helical lands 40 and 42which have bearing surfaces 44 and 46. As with the instrumentillustrated in FIGS. 1-3, points C and D distal from tissue removingedges 36 and 38, respectively, form about acute angles with linestangent to the periphery at the points of intersection as describedabove with reference to FIG. 2.

The working portions of endodontic instruments according to theinvention may be provided with various other friction reducing designsin lieu of or in addition to the above described designs illustrated inFIGS. 1-4C. Such designs may include flutes with receding surfaces asdescribed above, one or more recessed land portions, three or morespaced apart helical lands wherein the spacing between adjacent helicallands in cross-section varies, three or more spaced apart helical tissueremoving edges, various cutting edge designs or a combination of two ormore of the foregoing collection means. Cross-sectional configurationsof endodontic instruments having alternative designs are illustrated inFIGS. 5A through 16C.

In FIGS. 5A through 6C, the working portion 14 of instrument 10 containsat least one outer helical land 58 adjacent the periphery defined bytissue removing edge 64 and edge 62 distal from the tissue removing edge64 and at least one recessed land 54. As illustrated in FIG. 5B, helicalland 52 has a receding wall portion 54 extending from a shoulder 57 tothe flute 66 and which is a radial distance R₁ from the cross-sectionalcenter 56 of the working portion and a portion 58 which is adjacent theperiphery 60 of the working portion which is at a radial distance R₂from the cross-sectional center 56. The periphery 60 is defined byhelical tissue removing edges 64 and land portion 58. In thisembodiment, helical flutes 66 and 68 are equally spaced apart abouthelical land 52 and tissue removing edge 64.

In FIG. 6A-C, there is again a helical land 70 having at least one outerportion 76 and at least one recessed portion 72. The recessed portion 72which is at a radial distance R₁ from the cross-sectional center 74 ofthe working portion and a portion 76 of land 70 is adjacent theperiphery 78 of the working portion at a radial distance R₂ from thecross-sectional center 74. The periphery 78 is defined by helical tissueremoving edge 82 and point 80 distal from tissue removing edge 82. Inthis embodiment, the curvilinear distance between tissue removing edge82 and point 80 of helical land 70 is greater than the curvilineardistance between tissue removing edge 82 and point 88 of helical land70.

In the embodiments illustrated in FIGS. 5 and 6, there is a reduction ofthe force of tissue removing edges 64 and 82 against the wall of theroot canal in the direction perpendicular to the direction of rotationof the instrument in the canal because of the recessed portions 54 and72 of helical lands 52 and 70. A reduction in force of the tissueremoving edges 64 and 82 with respect to the canal wall provides areduction in friction during rotation of the instrument in the rootcanal as the instrument bends to conform to contours of the root canalcavity. The recessed wall portions of the helical lands have a radius R₁which is from about 4 to about 30 percent less than radius R₂.

In addition to the recessed wall portions illustrated in FIGS. 5A-C, theinstrument illustrated in FIGS. 6A-C also contains tissue removing edge82 which is a greater curvilinear distance from 80 than from point 88 onhelical land 70. The unequal curvilinear distances provide unequalcutting forces along the periphery 78 of the working portion of theinstrument thereby producing a side-cutting effect which more readilymaintains the central axis of a curved root canal.

FIGS. 7A through 8C are alternative embodiments of the inventioncontaining one or more helical flutes which have flute surfaces, incross-section which recede from the periphery at from about an acuteangle with respect to a line tangent to an inside periphery 102 at thepoint of intersection and one or more helical lands having recessed wallportions. The inside periphery 102 is defined by point E and recessedland portion 106. In FIGS. 7A-C, there is one helical flute 90 having atissue removing edge 98 which intersects an outer periphery 92 of theworking portion in the region immediately adjacent the outer periphery92 of the working portion at an angle of about 90 degrees to tangent toform a zero or neutral rake angle from the perspective of the surface 94of the flute 90.

Helical land 96 provides a bearing surface 106 between point E andtissue removing edge 98 so that when rotated in a canal, only edge 98removes tissue while the bearing surface 106 bears against the canalwall. Helical land 96 has an outer land portion 108 adjacent theperiphery 92 and a recessed land portion 106 between shoulder F andpoint E. Recessed land portion 106 has a cross-sectional radius R₁ fromthe cross-sectional center 104 of the working portion and outer landportion 108 has a radius of R₂ from the cross-sectional center 104 whichis from about 4 to about 30 percent greater than radius R₁.

As illustrated by FIG. 7B, the surface 94 of flute 90 which, incross-section, recedes from the inner periphery 102 at from about anacute angle with respect to a line tangent to the periphery 102 at thepoint of intersection as illustrate by FIG. 2 above. Flute 90 providesmeans for collecting and removing tissue or debris from the root canalby transporting the debris opposite to the direction of travel of theinstrument as the instrument is rotated in the root canal. Incombination with recessed wall portion 106 of helical land 96, theinstrument 10 illustrated in FIGS. 7A-C provides reduced friction as theinstrument is rotated in the canal due to uneven cutting forces and moreeffective tissue removal during endodontic procedures.

In FIGS. 8A-C, the endodontic instrument contains two helical flutes 110and 112 and two helical lands 114 and 116. Helical flutes 110 and 112,as illustrated in FIG. 8B, have surfaces 118 and 120 which recede fromthe inner peripheries 122 and 122' with about acute angles with respectto lines tangent to the peripheries 122 and 122' at the points ofintersection 132 and 134 thereof. Outer land portions 124 and 126 ofhelical lands 114 and 116 lie on the outer periphery 127 of the workingportion of the instrument which is defined by tissue removing edges 128and 130, while recessed wall portions 125 and 129 of helical lands 114and 116 lie at a radial distance R₁ from the cross-sectional center 131which is about 4 to about 30 percent less than radial distance R₂ fromthe center 131 to the periphery 127 of the working portion defined bytissue removing edges 128 and 130.

FIGS. 9A-C illustrate another instrument 10 according to the inventionhaving a working portion 14 containing two diametrically opposed helicalflutes 140 and 142 and two diametrically opposed helical lands 144 and146. In this embodiment, land 146 is an outer land which is adjacent theouter periphery 152 defined by tissue removing edge 154 and land 144 isa recessed land which is adjacent an inner periphery 150 defined bytissue removing edge 156 as illustrated by FIG. 9B. Recessed land 144has a radius R₁ from the cross-sectional center 148 to recessed landportion on inner periphery 150 and outer land 146 has a radius R₂ fromthe cross-sectional center 148 to outer periphery 152 which is 4 to 30percent greater than distance R₁. An instrument of the designillustrated in FIGS. 9A-C will provide less aggressive tissue removingforce with respect to the root canal wall on removing edge 154 as aresult of the recessed land portion 146 than the force of removing edge156. While helical flutes 140 and 142 are illustrated as being equallyspaced with respect to removing edges 154 and 156 about the peripheriesof the working portion, it will be recognized that unequal spacing ofthe flutes may also be used.

FIGS. 10A-C represent an instrument 10 according to the invention havinga helical land 170 which lies on the periphery 172 of the workingportion defined by tissue removing edge 190 and a helical land 174having a recessed wall portion 176 which has a radius R₁ at point 178with respect to the cross-sectional center 180 and a wall portion havinga radius R₂ which lines on the periphery 172. The radius of the wallportion of helical land 174 gradually increases from point 178 whichlies adjacent the inner periphery 184 to point 182 which lies adjacentthe outer periphery 172 so that helical land 174 has an outer landportion and a recessed land portion as illustrated in FIG. 10B. Therecessed portion 176 of land 174 provides a redacting in the cuttingforce of cutting edge 190 and therefore reduces the friction withrespect to the root canal walls during rotation of the instrument.

Spaced apart helical flutes 186 and 188 of the instrument illustrated inFIGS. 10A-C each have surfaces 194 and 196, in cross section, whichrecede at about acute angles to lines tangent to the peripheries 172 and184 at the points 182 and 178 respectively. FIGS. 10A-C thereforerepresent an endodontic instrument 10 containing a combination of arecessed land and the helical flutes described in FIGS. 1-3 whichreduces friction and/or has better removal efficiency of material fromthe root canal during an endodontic procedure.

FIGS. 11 A-C provide a variation of the endodontic instrument of theinvention which combines the features illustrated and described byreference to FIGS. 9A-C above with recessed land portions. In FIG. 11B,there are two opposing helical lands 200 and 210 separated by helicalflutes 224 and 226. Helical land 200 has a recessed wall portion 212 andan out wall portion 216 and helical land 210 has a recessed wall portion214 and an outer wall portion 218. The recessed wall portions 212 and214 lie on an inner periphery 236 defined by points 230 and 234 whichare distal to tissue removing edges 228 and 232. The recessed portions212 and 214 are at a radial distance of R₁ in cross section from thecross-sectional center 222 of the working portion and outer landportions 216 and 218 lie at a radial distance R₂ from the center 222 andadjacent an outer periphery 220 of the working portion defined by tissueremoving edges 228 and 232. Radius R₂ is at a distance which is 4 to 30percent greater than R₁ with respect to the center 222. Helical flutes224 and 226 are disposed about the periphery of the working portion sothat the curvilinear distance between tissue removing edge 228 and point230 is substantially the same as the curvilinear distance between tissueremoving edge 232 and point 234. However, unequal curvilinear flutedistances may also be used for increased cutting efficiency as describedabove with respect to FIGS. 6A-C.

FIGS. 12A-C, illustrate a combination of the features illustrated byFIGS. 1-3 with unequally spaced flutes 240 and 242 illustrated by FIGS.6A-C and unequally sized opposing lands 244 and 246. According to thisembodiment, the working portion 14 contains at least one helical flute240 wherein point 252 distal from tissue removing edge 250, incross-section, recedes at about an acute angle with respect to a linetangent to the periphery 248 at the point of intersection as shown inFIG. 12B and described with reference to FIGS. 1-3 above. As illustratedby FIG. 12B, the curvilinear distance from tissue removing edge 254 topoint 252 is greater than the curvilinear distance from tissue removingedge 250 to point 256. Hence the bearing surface 258 of helical land 246is substantially greater than the bearing surface 260 of helical land244. The unequal bearing surfaces of the lands provide unequal tissueremoval efficiencies along the periphery 248 of the working portion ofthe instrument thereby producing a side-cutting effect which morereadily maintains the central axis of a curved root canal.

A combination of two of the before mentioned embodiments of theinvention is illustrated in FIG. 13A-C. With reference to FIGS. 13B, theendodontic instrument 10 contains two helical lands 262 and 264 and twohelical flutes 266 and 268. Helical flute 266 is between tissue removingedge 272 and point 274 distal to removing edge 272 and helical flute 268is between tissue removing edge 276 and point 278 distal to removingedge 276. Points 274 and 278 recede at from about acute angles withrespect to line tangent to the periphery 270 at the points ofintersection therewith as described by reference to FIG. 2 above. Thecurvilinear distances along the periphery 270 of the working portionfrom tissue removing edge 272 to point 274 may be substantially the sameas the curvilinear distance from removing edge 276 to point 278 asillustrated, or the distances may be unequal.

In the illustrated embodiment of FIGS. 13A-C, there are also providedtwo helical flutes 280 and 282 between tissue removing edges 284 and 272and between tissue removing edges 286 and 276 which are substantiallysmaller in volume than flutes 266 ad 268. Again, the curvilineardistance between tissue removing edges 272 and 284 may be substantiallythe same as the curvilinear distance between tissue removing edges 286and 276 or the distances may be unequal.

The endodontic instrument 10 illustrated in FIGS. 14A-C, contains threespace apart tissue removing edges 290, 292 and 294 defining the workingportion periphery 296. Helical flute 298 lies between tissue removingedges 290 and 292, helical flute 300 lies between tissue removing edges292 and 294 and helical flute 302 lies between tissue removing edges 294and 290 such that the curvilinear distance along the periphery 296 fromremoving edge 290 to removing edge 292 is greater than the curvilineardistance from removing edge 292 to removing edge 294 which in turn isgreater than the curvilinear distance from removing edge 294 to removingedge 290. In the alternative, the curvilinear distances between removingedges 292 and 294 and removing edges 294 and 290 may be substantiallythe same. In another alternative, flutes 298, 300 and 302 are all ofsubstantially equal volume.

FIGS. 15A-C represent yet another embodiment of an instrument 10according to the invention which contains a combination of helical flutedesigns and one or more recessed helical land portions. In FIGS. 15A-C,there are two helical lands 310 and 312 each having outer land portions320 and 322 adjacent the periphery 324 defined by tissue removing edge338 and recessed land portions 314 and 316 which lie at a radialdistance R₁ from the cross-sectional center 318 of the working portion14 as illustrated in FIG. 15B. Helical land portions 320 and 322 andhelical land 326 all lie adjacent the periphery 324 of the workingportion at a distance R₂ from the cross-sectional center 318. In thisembodiment, helical land 326 does not contain a recessed land portion,however all three lands 310, 312 and 326 may contain recessed landportions.

In the instrument illustrated by FIG. 15B, there are three helicalflutes 328, 330 and 332. Helical flute 328 lies between tissue removingedge 334 and point 340 distal to removing edge 334, helical flute 330lies between tissue removing edge 336 and point 342 distal to removingedge 336 and helical flute 332 lies between tissue removing edge 338 andpoint 344 distal to removing edge 338. As described above with referenceto FIG. 2, points 340 and 342 recede at from about an acute angle withrespect to lines tangent to the periphery 324 at the point ofintersection thereof. Furthermore, the curvilinear distance from tissueremoving edge 338 to point 344 is greater than the curvilinear distancefrom tissue removing edge 334 to point 340 which in turn is greater thanthe curvilinear distance between tissue removing edge 336 and point 342.Accordingly, this embodiment combines the recessed land features withthe flutes of FIGS. 1-3 and the unequal spacing between adjacent flutesof FIGS. 6A-C.

FIGS. 16A-C provide another design of an endodontic instrument 10 of theinvention. In this design, there are three helical flutes 350, 352 and354 in the working portion 14 and three spaced apart helical lands 356,358 and 360. The curvilinear distance along the periphery 362 of theworking portion from tissue removing edge 366 to point 364 distal toremoving edge 366 is substantially greater than the curvilinear distancefrom tissue removing edge 370 to point 368 as shown in FIG. 16B.Likewise, the curvilinear distance along the periphery 362 from tissueremoving edge 374 to point 372 is greater than the curvilinear distancefrom removing edge 370 to point 368 and may be the substantially thesame, greater than or less than the curvilinear distance from tissueremoving edge 366 to point 364. In this embodiment, the surfaces 376,378 and 380 of flutes 350, 352 and 354 are angular rather than roundedwhen viewed in cross-section (FIG. 16B).

As described above with reference to FIG. 2, the points 364, 368 and 372distal from removal edges 366, 370 and 374 respectively recede at aboutacute angles with respect to a line tangent to the periphery at thepoints of intersection therewith. Accordingly, the instrumentillustrated by FIGS. 16A-C provide tissue removal efficiencies along theperiphery 362 of the working portion which are enhanced by producing aside-cutting effect which more readily maintains the central axis of acurved root canal.

The endodontic instruments of the invention provide reduced resistanceduring endodontic procedures and/or improved removal of material fromthe root canal of a tooth because of their design. The endodonticinstruments of the invention are also believed to possess improved sidecutting capability and an inherent propensity to work into canal areasthat are noncircular so as to remove material from nooks previouslyuntouched or insufficiently worked by conventional instruments, as wellas to reduce the propensity for the instruments to break duringendodontic treatment procedures.

For additional strength, it is preferred that diameter of the web, oruncut core portion of the endodontic instruments of the invention befrom about 10 to about 80 percent of the cross-sectional diameter of theworking portion. Web diameters greater than about 80 percent may makethe instruments too rigid to bend around the curved portions of the rootcanal while core diameters of less than about 10 percent may not berigid enough to provide effective cutting or compacting of material inthe root canal.

The endodontic instruments of the invention may be used by manipulatingthe instrument manually in a rotating action, or the instrument may bemanipulated by attaching the proximate end (FIG. 1) of the instrument toa motorized device for effecting the removal of material in the rootcanal.

The rake angles of the tissue removing edges may be positive, negative,or neutral, but are preferably about neutral with respect to theperiphery of the working portion. In order to make the instrumentshaving the desired rake angles and configurations, the instruments maybe ground from a straight or tapered rod, twisted and/or drawn to ataper with or without grinding.

The endodontic instruments of the invention are preferably made formsurgical stainless steel, however, they can also be made from compositematerials such as nickel titanium or other "exotic" alloys and the like.The preferred material for the instruments of the invention is nickeltitanium or titanium 13-13. Those of ordinary skill will recognize thattechniques for making conventional instruments may generally be appliedto the manufacture of instruments according to the invention and withvarious known or later-developed materials. Suitable grinding techniqueswhich may be used are described in metallurgical texts for grindingmetals. For example, it is known that certain grinding wheels or bitsfor making instruments out of one material may not be effective forother or different materials. While a grinding surface made of coursegrit and rotating at a relatively high speed may be suitable forgrinding stainless steel or a hard metal shaft, a nickel-titanium shaftmay require a finer grit grinding surface rotating at a relativelyslower speed in order to effectively abrade the shaft to form thenecessary edges and lands.

The foregoing detailed description is given for understanding of theinvention and to illustrate its various features and known advantages,but no unnecessary limitations are to be understood therefrom.Modifications of the various illustrated embodiments and, indeed, thefashioning of other or even improved embodiments, some of which may beobvious to those skilled in the art upon reading the disclosure, may bemade without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. An endodontic dental instrument comprising:ashaft; an elongate working portion along at least a portion of thelength of said shaft; and at least two helical, parallel flutes formedin the working portion of said shaft defining corresponding tissueremoving edges substantially at the periphery of said working portion,said tissue removing edges being substantially unequally spaced apartabout the periphery of said working portion so as to provide unequalcutting forces along the periphery of said working portion when saidinstrument is rotated in a root canal; whereby said instrument morereadily maintains the central axis of a curved root canal.
 2. Theendodontic instrument of claim 1 wherein said flutes have substantiallyunequal dimensions when viewed in transverse cross-section.
 3. Theendodontic instrument of claim 1 wherein said flutes are substantiallyunequally spaced apart about the periphery of said working portion. 4.The endodontic dental instrument of claim 1 further comprising at leastone outer land portion at the periphery of said working portion adjacenteach said tissue removing edge and at least one recessed land portion.5. The endodontic dental instrument of claim 4 wherein the recessed landportion has a radius from a cross-sectional center of the instrument tothe recessed land portion which is about 4 to 30 percent less than aradius from the cross-sectional center of the instrument to theperiphery of the working portion.
 6. The endodontic instrument of claim1 wherein each flute defines at least one point distal from each saidtissue removing edge defining a trailing edge of each said flute, eachsaid trailing edge being undercut so as to improve the chip removalcapacity of said instrument.
 7. An endodontic dental instrumentcomprising:a shaft; an elongate tapered working portion along at least aportion of the length of said shaft; at least two helical flutes in theworking portion of said shaft defining corresponding tissue removingedges at the periphery of said working portion of said shaft, saidflutes having a concave shape when viewed in cross-section; an outerland portion at the periphery of said shaft between adjacent flutes; anda recessed land portion recessed from the periphery of said shaftbetween adjacent flutes.
 8. The endodontic dental instrument of claim 7wherein the recessed land portion has a substantially constant radiusfrom a cross-sectional center of the instrument to the recessed landportion which is about 4 to 30 percent less than a radius from thecross-sectional center of the instrument to the periphery of the workingportion.
 9. The endodontic instrument of claim 7 wherein said tissueremoving edges are unequally spaced apart about the periphery of saidworking portion so as to provide unequal cutting forces along theperiphery of said working portion when said instrument is rotated in aroot canal whereby said instrument more readily maintains the centralaxis of a curved root canal.
 10. The endodontic instrument of claim 7wherein said flutes have substantially unequal dimensions when viewed intransverse cross-section.
 11. The endodontic instrument of claim 7wherein said flutes are substantially unequally spaced apart about theperiphery of said working portion.
 12. The endodontic instrument ofclaim 7 wherein each flute defines at least one point distal from eachsaid tissue removing edge defining a trailing edge of each said flute,each said trailing edge being undercut so as to improve the chip removalcapacity of said instrument.
 13. An endodontic dental instrumentcomprising:a shaft; an elongate working portion along at least a portionof the length of said shaft; and at least two helical flutes formed inthe working portion of said shaft, each said flute defining a tissueremoving edge substantially at the periphery of said working portion anda point distal from each said tissue removing edge defining a trailingedge of each said flute, each said trailing edge being undercut toprovide increased chip removal capacity when said instrument is rotatedin a root canal.
 14. The endodontic instrument of claim 13 wherein saidtissue removing edges are unequally spaced apart about the periphery ofsaid working portion so as to provide unequal cutting forces along theperiphery of said working portion whereby said instrument more readilymaintains the central axis of a curved root canal.
 15. The endodonticdental instrument of claim 13 further comprising at least one outer landportion at the periphery of said working portion adjacent each saidtissue removing edge and at least one recessed land portion.
 16. Theendodontic dental instrument of claim 15 wherein the recessed landportion has a radius from a cross-sectional center of the instrument tothe recessed land portion which is about 4 to 30 percent less than aradius from the cross-sectional center of the instrument to theperiphery of the working portion.